When seeking information regarding the characteristics of an earth formation, such as, for example, the degree to which it is saturated in hydrocarbons, a core sample may be obtained from the earth formation. The core sample may then be analyzed to determine the characteristics of the earth formation. Core samples may be obtained using coring tools. A coring tool may include an inner barrel assembly located with an outer barrel in a manner such that the outer barrel, having a core bit at a bottom thereof, may rotate about a longitudinal axis of the coring tool while an inner barrel, having an inner bore for receiving the core sample, remains substantially rotationally stationary within the outer barrel. The core bit may include an inner bore and a cutting structure surrounding the inner bore. In many instances, the outer barrel is assembled section by section into a pre-drilled wellbore, and thereafter the inner barrel assembly is assembled section by section within the outer barrel until the inner barrel assembly is fully assembled and located in a longitudinally fixed but rotationally free, fully operational “coring” position relative to the outer barrel.
As the coring tool is driven into an earth formation, the core bit may remove earth material around a core sample, which is received into the inner bore. The inner barrel may extend longitudinally above the inner bore of the core bit. The core sample may be received into the inner barrel, and may be retained in the inner barrel by a core catcher to keep the core sample within the inner barrel as the coring tool is withdrawn from the borehole. As the core sample extends into the inner barrel, the core sample may contact a portion of the inner barrel and cause a significant increase in friction between the core sample and the inner barrel or even completely lock the core sample to the inner barrel. Such occurrences are often referred to in the art as “jamming.” When jamming occurs during a coring operation, the operation must be terminated and the drill string tripped out from the wellbore. Jams may be caused by a number of factors. For example, a condition known in the art as “formation fault slant” may cause a wedging jam between the core sample and the inner barrel. Additionally, jams may be caused by collapse of unconsolidated core material or expansion of clay or other materials inside the core sample. In some instances, jams occur undetected, resulting in the core sample failing to enter the inner barrel as the coring tool continues to engage uncut formation material. In such instances, the core sample may inadvertently be destroyed as the jammed portion of the inner barrel grinds or mills away the core sample as the coring tool progresses downward into the formation. The information obtained from core samples is valuable for understanding the subterranean formation properties and conditions. Thus, jams resulting in a shortened coring run and/or a destroyed core sample and/or a core sample shorter than the maximum retrievable length result in loss of information, time and money.